He’d heard a radio report about the injured dolphin they rescued from a crab trap and wanted to see if he could build the animal a prosthetic tail to replace the one that had been amputated.

“They just thought I was some smart [aleck],” recalls Carroll.

But Carroll, a native of Ireland who is one of the world’s leading prosthetists, convinced the dolphin’s caretakers of his credentials and drove from Orlando to meet with them that day.

The 3-month old dolphin, named Winter because she was found on a particularly cold December day in 2005, immediately stole Carroll’s heart. In time she would steal hearts around the world and inspire the new movie “Dolphin Tale,” in which she plays herself alongside co-stars Harry Connick Jr., Morgan Freeman and Ashley Judd.

“She reminded me of the children I see who are just after having an amputation,” recalls Carroll of his first meeting with the bottlenose dolphin. “Obviously Winter was very sick, badly injured. And the people at the aquarium, their hearts were broken. . . . They were just incredible with her, working 24/7. There was never a moment that Winter was without human contact. They were now her adopted family.”

Carroll and a colleague, Dan Strzempka, both prosthetists with Hanger Orthopedic Group who happened to live in Florida, quickly committed themselves to the project. They had built prosthetics for birds, horses and dogs before, but never a dolphin.

Carroll and Strzempka, working pro bono, first had to figure out whether a fake tail would even help Winter. The dolphin could still swim on her own, despite losing her entire tail and two vertebrae. She had adapted, learning to swim side to side, the way a fish or shark would, rather than with the up-and-down motion natural to dolphins.

She couldn’t swim as fast or jump as high as most dolphins, but the real problem was that she was slowly damaging her spine. “She started to develop scoliosis,” says Carroll. “So we felt that by fitting her with a prosthetic device, we could get her swimming in an anatomically correct manner again.”

The challenges in creating such a device were manifold. The sockets of most prosthetics fit over arm or leg bones, and need not be flexible. This one would attach to the end of Winter’s body, and had to move side to side, up and down and gently twist as she swam.

It also needed to attach securely to her stump. This was particularly difficult, Carroll explains, because Dolphins have hypersensitive skin. “Human skin is fragile, but I can scratch my nail across my skin and in a couple of minutes that mark is gone,” he says. “But if I put that same mark on the dolphin’s skin, six weeks later I’d come back and that mark would still be there.”

They initially tried a silicone-based material as the adhesive lining for the prosthetic. Because Winter didn’t have the ability to articulate what was painful or irritating for her, they used heat-detecting cameras to pinpoint areas of sensitivity and found that with the silicone, she was developing hot spots of discomfort.

Carroll and Strzempka, an amputee who lost his own leg in a lawn-mowing accident as a child, went back to the drawing board and worked with a chemical engineer to develop a new material, nicknamed “WintersGel,” that would distribute the pressure more evenly.

Strzempka tested it on himself first and when they put it on Winter, they didn’t pick up any hot spots. The team began preparing the dolphin for her new prosthetic, starting with a very small tail so she slowly become reaccustomed to the sensation of its resistance in the water. Trainers acted as physical therapists, coaching her to once again move her body up and down. Over the course of a year, the team gradually increased the size of the tail to match her now 230-pound body, and Winter began swimming as she had before the accident.

“We knew it was going to happen, but when it happened, it was just awesome,” Carroll says of the first time Winter used the full prosthetic. “Just to see this very clean, anatomically correct, fluidlike motion in the water — it was absolutely breathtaking.”

Eventually, the prosthetists realized WintersGel would work on humans. Carroll recalls one child in particular who benefited from the innovation. The 9-year-old girl had been badly burned as a baby and had to have her legs amputated. She wouldn’t wear her prosthetics because they were too painful against her sensitive scar tissue, so she was using a wheelchair. Carroll met with her, told the little girl about Winter and fitted her with a new sleeve made of WintersGel. “So now, a year and a half later, she’s flying around,” on her prosthetic legs, says Carroll.

Working with Winter has become a hobby for Carroll and Strzempka, who still visit her at the Clearwater Aquarium at least once a month. The facility itself was nearing bankruptcy when Winter arrived but has since become a major tourist attraction, undergoing significant renovations and luring thousands of visitors, including many wounded soldiers and children with disabilities. A children’s book about her story, “Winter’s Tale: How One Little Dolphin Learned to Swim Again,” was published in 2009.

Carroll and Strzempka also worked as advisers on the movie, which opened in theaters Friday. The fictionalized film plants a young boy and his family at the center of the story but closely adheres to the technical evolution of Winter’s prosthetic.

When Carroll and Strzempka learned there would be a movie, they began joking about who would play each of them in the film. They never dreamed they’d be combined into one character and cast as Morgan Freeman.

“Some people talk about a bucket list, but here you go,” says Carroll. “My bucket list has come true.”

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